This invention generally relates to feedstocks for lactating dairy cows which are nutrient-supplemented to provide milk with a modified fatty acid profile. More specifically this invention relates to the production of cow milk which has an increased content of conjugated linoleic acid (CLA).
Conjugated linoleic acid is a collective term for positional and structural isomers of linoleic acid. These isomers are combinations of delta-9,11 or delta-10,12, with each of the two double bonds having the possibility of being cis or trans. Thus, there are eight isomers with these specific combinations. The conjugated linoleic acid isomer with a cis double bond between carbon atoms 9 and 10, and a trans double bond between carbon atoms 11 and 12, is of particular interest for purposes of the present invention.
The nomenclature of fatty acids is simplified by referring to stearic acid as 18:0, oleic acid as cis-9 18:1, linoleic as cis-9, cis-12 18:2, and conjugated linoleic acid, for example, as cis-9, trans-I 11 18:2.
Over 400 different fatty acids have been identified in dairy cow milk fat, but only a limited number occur in concentrations greater than 1%. Typical fatty acid constituents of cow milk fat are listed as a percentage of total milk fat in TABLE I.
The effects of different feedstocks on the milk fat profile of cow milk has been extensively studied, and correlations have been established. One effect is that dietary fats increase the proportions of long-chain fatty acids in milk fat. By feeding supplemental fats with different relative amounts of 16 or 18 carbon fatty acids to lactating cows, the chain length of predominant fatty acids in milk fat can be influenced. For example, feeding a dietary fat containing a high proportion (50%) of 16:0 carbon fatty acid will increase 16:0 in milk fat. Similarly, feeding dietary 18:1 fatty acid will increase 18:1 fatty acid in milk fat.
Many dietary fats contain a large proportion of unsaturated fatty acids. Under the usual feeding conditions for lactating cows, however, these unsaturated fatty acids do not appear in cow milk because they are extensively biohydrogenated to more saturated fatty acids (e.g., stearic acid) by the ruminal microbial population.
Partial biohydrogenation yields various unsaturated isomers that can be absorbed and incorporated in milk fat. Two of the most important partially biohydrogenated isomers are trans-11 18:1 and cis-9, trans-11 18:2 (conjugated linoleic acid, CLA).
Traditionally, milk fat has been condemned as not being xe2x80x9cheart healthyxe2x80x9d because of its high content of cholesterol and saturated fatty acids. More recent investigations suggest that the cholesterol content is of relatively small concern and that only certain saturated fatty acids, i.e., lauric (12:0), myristic (14:0) and palmitic (16:0), consistently raise plasma cholesterol in susceptible people.
Recent research also has shown that there are numerous components of milk fat that are potential anticarcinogenic agents [J. Nutr., 127, 1055 (1997)]. These include CLA, sphingomeyelin, butyric acid, and ether lipids. CLA is of the greatest interest. This CLA isomer of linoleic acid, formed mainly as a product of the ruminal biohydrogenation process, is the most potent natural anticarcinogen in foods [Cancer (Suppl.),74, 1050 (1984)]. CLA occurs in milk fat in a quantity of about 0.3-0.8% of the total milk fat.
In addition to its anticarcinogenic effects, CLA has been reported to influence body composition (less fat, more muscle), improve bone growth, and stimulate immune function.
There is continuing interest in the development of new methods and feedstocks for producing dairy products that are healthier for human consumption.
Accordingly, it is an object of this invention to provide a dietary feedstock supplement for lactating dairy cows.
It is another object of this invention to provide a dietary ration for feeding lactating dairy cows, which will effect a beneficial modification of the fatty acid profile of the cow milk fat.
It is a further object of this invention to provide cow milk which has an elevated content of conjugated linoleic acid, and an increased ratio of 18:1 to 18:0 fatty acids.
Other objects and advantages of the present invention shall become apparent from accompanying description and example.
Of background interest, with respect to the present invention, are publications which describe dietary fat supplements for ruminants, which include U.S. Pat. Nos. 4,642,317; 4,729,896; 4,826,694; 4,853,233; 4,909,138; 5,182,126; 5,212,325; 5,221,544; 5,236,723; 5,250,714; 5,456,927; 5,496,572; 5,547,686; 5,585,134; 5,670,191; and publications cited therein; incorporated by reference.
Other publications of interest include J. Food Sci., 61 (No.1), 24 (1996) which describes the feeding of calcium salts of high oleic su nflower oil (HOSxe2x80x94Ca) to lactating cows to yield cow milk with an increased content of oleic acid.